Substituent Effects on Xenon Binding Affinity and Solution Behavior of Water-Soluble Cryptophanes

Hill, P. Aru; Wei, Qian; Troxler, Thomas; Dmochowski, Ivan J.

doi:10.1021/ja8100566

Cited by 78 publications

(95 citation statements)

References 46 publications

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“…With a water-soluble triacetate-functionalized cryptophane derivative, a much higher affinity for xenon is observed (K = 33 000 M −1 ). 32 Part of this dramatic increase can be ascribed to a hydrophobic effect of high-energy water 6 inside the cryptophane. With larger solvents such as 1,2-dichlorobenzene, a much higher association constant of K = 2.6 × 10 4 M −1 between the cryptophane 1 (n = 3) and even chloroform was observed.…”

Section: Stacking and Dispersive Interactions In Selected Supramolecumentioning

confidence: 99%

Dispersive Interactions in Solution Complexes

Schneider

2015

Acc. Chem. Res.

112

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Dispersive interactions are known to play a major role in molecular associations in the gas phase and in the solid state. In solution, however, their significance has been disputed in recent years on the basis of several arguments. A major problem until now has been the separation of dispersive and hydrophobic effects, which are both maximized in water due the low polarizability of this most important medium. Analyses of complexes between porphyrins and systematically varied substrates in water have allowed us to discriminate dispersive from hydrophobic effects, as the latter turned out to be negligible for complexations with flat surfaces such as porphyrins. Also, for the first time, it has become possible to obtain binding free energy increments ΔΔG for a multitude of organic residues including halogen, amide, amino, ether, carbonyl, ester, nitro, sulfur, unsatured, and cyclopropane groups, which turned out to be additive. Binding contributions for saturated residues are unmeasurably small, with ΔΔG > 1 kJ/mol, but they increase to, e.g., ΔΔG = 5 kJ/mol for a nitro group, a value not far from, e.g., that of a stacking pyridine ring. Stacking interactions of heteroarenes with porphyrins depend essentially on the size of the arenes, in line with polarizabilities, and seem to be rather independent of the position of nitrogen within the rings. Measurements of halogen derivatives indicate that complexes with porphyrins, cyclodextrins, and pillarenes as hosts in different media consistently show increasing stability from fluorine to iodine as the substituent. This, and the observed sequence with other substrates, is in line with the expected increase in dispersive forces with increasing polarizability. Induced dipoles, which also would increase with polarizability, can be ruled out as providing the driving source in view of the data with halides: the observed stability sequence is opposite the change of electronegativity from fluorine to iodine. The same holds for the solvent effect observed in ethanol-water mixtures. Dispersive contributions vary not only with the polarizability of the used media but also with the interacting receptor sites; it has been shown that for cucurbiturils the polarizability inside the cavity is extremely low, which also explains why hydrophobic effects are maximized with these hosts. Complexations with other known host compounds, however, such as those between cryptands or cavitands with, e.g., noble gases, bear the signature of dominating dispersive forces. Some recent examples illustrate that such van der Waals forces can also play an important role in complexations with proteins. Again, a clue for this is the increase in ΔG for inhibitor binding by 7 kJ/mol for, e.g., a bromine in comparison to a fluorine derivative.

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Section: Stacking and Dispersive Interactions In Selected Supramolecumentioning

confidence: 99%

Dispersive Interactions in Solution Complexes

Schneider

2015

Acc. Chem. Res.

112

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“…If water is used as solvent, the binding constants can be drastically increased. For example, a water-soluble triacetate-functionalized cryptophane-A derivative shows the highest affinity for xenon which was ever measured for a host molecule (K i ¼ 33,000 M À 1 at 293 K in buffer) 15 . This increase is explained by entropic (hydrophobic) effects that likely involve desolvation of xenon clathrates upon complexation.…”

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confidence: 98%

Strongly underestimated dispersion energy in cryptophanes and their complexes

2014

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Cryptophanes, composed of two bowl-shaped cyclotriveratrylene subunits linked by three aliphatic linker groups, are prototypal organic host molecules which bind reversibly neutral small guest compounds via London forces. The binding constants for these complexes are usually measured in tetrachloroethane and are in the range of 10 2 -10 3 M À 1 . Here we show that tetrachloroethane is-in contrast to the scientific consensus-enclosed by the cryptophane-E cavity. By means of NMR spectroscopy we show that the binding constant for CHCl 3 @cryptophane-E is in larger solvents two orders of magnitudes higher than the one measured before. Ab initio calculations reveal that attractive dispersion energy is responsible for high binding constants and for the formation of imploded cryptophanes which seem to be more stable than cryptophanes with empty cavities.

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“…Recent X-ray crystallographic studies have shown that the internal volume of trisubstituted cryptophane-A derivatives can vary by more than 20%, depending on the size of the encapsulated guest (12). Several cryptophane-A derivatives have been synthesized and shown by isothermal titration calorimetry (ITC), fluorescence quenching, and NMR studies to exhibit xenon association constants as high as 33;000 AE 3;000 M −1 at 293 K in phosphate-buffered water (13)(14)(15)(16). Herein, we report a previously unsynthesized cryptophane-A derivative, tris-(triazole ethylamine) cryptophane (TTEC), with superior xenon-binding characteristics.…”

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confidence: 99%

Measurement of radon and xenon binding to a cryptophane molecular host

Jacobson

Khan²,

Collé³

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Xenon and radon have many similar properties, a difference being that all 35 isotopes of radon ( 195 Rn– 229 Rn) are radioactive. Radon is a pervasive indoor air pollutant believed to cause significant incidence of lung cancer in many geographic regions, yet radon affinity for a discrete molecular species has never been determined. By comparison, the chemistry of xenon has been widely studied and applied in science and technology. Here, both noble gases were found to bind with exceptional affinity to tris-(triazole ethylamine) cryptophane, a previously unsynthesized water-soluble organic host molecule. The cryptophane–xenon association constant, K a = 42,000 ± 2,000 M -1 at 293 K, was determined by isothermal titration calorimetry. This value represents the highest measured xenon affinity for a host molecule. The partitioning of radon between air and aqueous cryptophane solutions of varying concentration was determined radiometrically to give the cryptophane–radon association constant K a = 49,000 ± 12,000 M -1 at 293 K.

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Substituent Effects on Xenon Binding Affinity and Solution Behavior of Water-Soluble Cryptophanes

Cited by 78 publications

References 46 publications

Dispersive Interactions in Solution Complexes

Dispersive Interactions in Solution Complexes

Strongly underestimated dispersion energy in cryptophanes and their complexes

Measurement of radon and xenon binding to a cryptophane molecular host

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